Power switches are used e.g. in switched-mode power supplies, e.g. DC-to-DC power converters such as buck converters or SEPIC converters. Such power converters may be used within chargers for electronic devices (e.g. computing devices) which comprise a rechargeable battery and/or within driver circuits for SSL (solid state lighting) devices which comprise e.g. LEDs (light emitting diodes) and/or OLEDs (organic LEDs).
The power converters comprise a power converter network and one or more power switches, wherein the one or more power switches are typically operated in a switched on/off mode, such that energy is converted from an input side of the power converter to an output side of the power converter. The energy is typically provided by a mains power supply. For the operation of the one or more power switches a supply voltage Vcc may be required. The supply voltage Vcc for the one or more power switches may be provided using a supply voltage capacitor.
During start-up of the power converter, the supply voltage capacitor may need to be charged in order to provide the supply voltage Vcc. It is typically desirable to limit the size of the supply voltage capacitor (e.g. for size and cost reasons) and/or to limit the start-up current required to charge the supply voltage capacitor (e.g. for limiting the load to the mains voltage). Typically, the one or more power switches can only start normal operation once the supply voltage capacitor has been sufficiently charged to provide the supply voltage Vcc. This results in relatively long start-up times (e.g. in the range of seconds) for the one or more power switches and for the power converter.
The supply voltage capacitors may be charged using dedicated power transistors which are used upon start-up to couple the supply voltage capacitors to the (rectified) mains voltage. The use of dedicated power transistors for the start-up of a power converter is costly and it is therefore desirable to reduce the number of required power transistors.
The present document addresses the above mentioned technical problems. In particular, the present document describes an electronic circuit which is configured to charge a supply voltage capacitor from a mains supply (and to thereby generate a supply voltage for a power switch). The electronic circuit allows for low start-up time intervals and/or may be used in conjunction with low capacitance supply voltage capacitors. Furthermore, the electronic circuit enables use of the one or more power switches of the power converter for charging the supply voltage capacitor, thereby removing the need for additional dedicated power switches, i.e. thereby reducing the cost of the power converter.